Method of casting aluminum on ferrous base to form duplex structure



United States Patent one 2,881,491 Patented Apr. 14, 1959 METHOD OFCASTING ALUMINUM ON FERROUS BASE TO FORM DUPLEX STRUCTURE Walter E.Jominy, Detroit, and John H. Olson, Birmingham, Mich., and Robert B.Boswell, New Orleans, La., assignors to Chrysler Corporation, HighlandPark, M1ch., a corporation of Delaware No Drawing. Application March 23,1953 Serial No. 344,190

22 Claims. (Cl. 22-204) This invention relates to a process for formingcomposite or duplex metal structures, specifically aluminumferrous metalstructures by casting a layer of hot molten aluminum or its alloys to apreformed ferrous metal body or base such as of steel or iron andforming an integral alloy bond therewith.

More particularly, our invention relates to such a process in which afused flux of suitable salts and of such viscosity as to possess ease orfreedom of flow, that is to say, a liquid or fluent flux, is employed toeffect the alloy bonding of the aluminum with the ferrous metal.

The casting of aluminum to ferrous metal in a mold presents problems notencountered in the conventional aluminum coating procedures where aflux-treated ferrous member is immersed in a bath of the hot moltenaluminum to form a coating or predetermined layer of the latter thereon.In the mold casting process, the ferrous member instead of beingimmersed in a large mass of constantly heated molten aluminum, is placedin a suitable mold into which molten aluminum ladled from the furnace ispoured. A heavy cast layer of aluminum of substantial thickness isformed integral with the ferrous metal body and is of a thickness manytimes that obtained by coating steel with aluminum by immersion ordipping. Necessarily a loss of heat occurs on transfer, and a longertime interval transpires in the casting process during which the fluxmay cool before the aluminum reaches the flux-treated ferrous 'metal andfills the mold. Problems of heat exchange, therefore, arise which arenot usual in a coating procedure. Moreover, in a dip coating process, ifa suitable ductile alloy layer is to be obtained with the ferrous metal,the molten aluminum where prepared from substantially pure ingot, mustusually be employed at a temperature immediately above its melting point(1220 R). In a mold casting process, in order to secure an alloy bond,the temperature of the molten aluminum must be considerably higher thanits melting point and higher than the temperatures usually used in a dipcoating process. We have found that this feature makes possible agreater latitude in the temperature of the aluminum in operation.

Furthermore, it has heretofore been proposed to cast aluminum to aferrous metal body in a mold by a procedure wherein the ferrous body isfirst given a hot dip or flash coating of the aluminum. According tothis process, the ferrous body is first dipped in a bath of moltenaluminum and then transferred 'to a mold into which molten aluminum ofthe bath is then poured so that it contacts the flash-coated surface toform an alloy bond with the ferrous body.

The described process is at best only partially successful and has anumber of disadvantages. Unless the interior surfaces of the member aremasked with a suitable graphite wash to protect them from the aluminumbath they will alloy with the aluminum and leave undesired aluminumsurfaces that will have to be subsequently machined off. Also oxidizedareas form upon the ferrous metal surfaces during heating of the ferrousbody when it is immersed in the aluminum bath. The molten aluminum doesnot wet the ferrous surfaces in the oxidized areas, this even when thesurfaces are scraped to break through the oxide layers, and as a resultno alloy bond is obtainable between the cast aluminum and ferroussurfaces in these unwetted areas. Stated otherwise, it is difiicult bythe recited process to obtain a continuous aluminum flash coating, andthe cast layer of aluminum subsequently formed is not always providedwith a continuous alloy bond with the ferrous metal. Moreover, duringflash coating of the ferrous body, the molten aluminum of the bathdissolves some of the ferrous metal. This causes particles of a hardhigh melting point, ironaluminum alloy to accumulate :in the bath. Inorder to settle out these particles, the bath must be allowed to stand.This requires a holding period making extra furnace capacity necessary.If the particles are not permitted to settle out, they may be carriedwith the molten aluminum of the bath to the molds when it issubsequently poured to make the cast layers. There they form hard spotswhich make machining of the cast layer difiicult.

In seeking a more suitable procedure for successfully casting aluminumor its alloys to ferrous metal bodies in a mold, other methods wereconsidered and it 'was found that a continuous alloy bond between thecast aluminum and ferrous metal may be obtained by a process utilizing afluent fused flux composition. It was noted, however, that certainingredients are essential to the composition and that proper proportionsthereof, the temperature conditions under which the composition isemployed, and the time interval between removal of the ferrous body fromthe flux and the start of pouring ofthe molten aluminum are of acritical nature and necessary of careful control in order to obtain goodwetting properties and an acceptable continuous alloy bond between thealuminum and the ferrous metal.

For example, careful selection of the character of the flux compositionand of the operating temperatures is essential to avoid thin spots inthe protective flux layer or more extensive incomplete wetting of theferrous metal surfaces, either of which will permit oxidation of theferrous metal. Moreover, if the flux is too viscous, an excessive amountwill adhere to the ferrous surface and may not be easily washed out bythe molten aluminum during casting. If the flux is not completely washedoff, any remainders are likely -to produce unbonded spots between thealuminum and steel which will also be subject to subsequent corrosion.Improper temperature control of the operations, improper compositions,and too long a time interval between fluxing and pouring also contributeto solidification of the flux on the steel before pouring of thealuminum takes place. Where this occurs, the flux adheres to the ferrousmetal surface with considerable adhesion and must be melted by thealuminum before it can be washed off. This is unlikely to be complete.

Accordingly, it is an object of our invention to provide a process forcasting aluminum to ferrous metal bodies in a mold which utilizes afused flux composition that provides good wetting properties relative tothe ferrous metal surfaces to which the aluminum is to be .alloy bondedand which'will provide a layer of the flux of sufficient thickness tocompletely blanket these surfaces to eflectively protect them fromoxidation prior to pouring of the aluminum.

Another object is to provide such a process in which the ferrous metalsurfaces to which aluminum is to be directly bonded by casting are givena layer of fluent fused flux composition of sufiicient viscosity to beadherent and that will maintain its freely flowable character prior toand during pouring of the molten aluminum such that the latter can pushthe flux ahead of it, i.e., float the flux on top of it without leavingflux remainders as its level changes in the mold.

A further object is to provide such a process wherein the poured moltenaluminum will completely wet and cover the ferrous metal surfaces as itremoves the flux, and form a complete and continuous alloy bondtherewith.

An additional object is to provide fused flux compositions operable inthe aforesaid processes.

Another object is to provide a control system for compensating for lossof essential ingredients during operations.

Other objects will become apparent from the following description of thepreferred embodiments of our invention. For the purpose of illustrationonly, we will describe our invention as applied to casting collars ormuffs of aluminum on steel sleeves, and in particular to the making offorged alloy steel barrels with an aluminum muff which is to besubsequently machined to provide cooling fins for these barrels whichare to form the cylinders in air-cooled tank engines.

In carrying out our invention, we have discovered that the essentialbasic ingredients of the fused flux composition are sodium chloride(NaCl), potassium chloride (KCl), and natural Greenland cryolite (sodiumaluminum fiuoride-Na AlF When used in proper amounts, these salts makepossible a flux composition having excellent fiuxing properties. Tothese should preferably be added anhydrous zinc chloride (ZnCl which wehave discovered considerably improves the mixture by increasing itsviscosity. Other alkali salts such as calcium chloride (CaCl or otherfluorides Such as synthetic or reduction grade cryolite may optionallybe included by addition or substitution but in limited amounts as willbe hereinafter evident.

Broadly speaking, by our process, the ferrous metal members afterinitial treatment by known or hereinafter described procedures to insurethat their surfaces are clean and free from impurities, are immersed ina hot fluent fused flux bath (940-1l80 F. melting point) having atemperature preferably substantially not less than 1340 F. andpreferably not exceeding substantially 1450" F.

The amount of the essential ingredients to use may vary within certainpermissible limits depending upon the character of parts being treatedand the time elapsing between fluxing and start of pouring of thealuminum. For example, in some operations especially where the parts tobe treated have a relatively small surface area and can be rapidlyprocessed between flux treatment and casting, for example within 30seconds, the bath may contain a molten mixture of the followingessential ingredients in about the amounts stated:

Parts by weight Sodium chloride 7 to 40 Potassium chloride 24 to 44Natural Greenland cryolite 9 to 25 Zinc chloride 0 to 34 Although nozinc chloride has been used with success in certain compositions, it isgenerally found expedient to use at least a small amount of thisingredient for its viscosity control feature. However, if the amount ofzinc chloride exceeds about 25% by weight, excessive fuming may occur atthe higher temperatures and must be controlled. Moreover, cryolite above25% causes excessive sludging.

Where the ferrous metal surfaces to be treated are large and are notideal for bonding, or where a greater time period is required, forinstance up to about 40 seconds, between fluxing and casting, a somewhatcloser range of ingredients is desirable. In such cases the followingrange of essential ingredients will be found to be preferable:

Parts by weight The parts are preferably kept immersed in the flux bathat least until they attain a temperature about that of the bathtemperature and are then removed. Such time of immersion is sufiicientto provide a substantial layer of the fluent flux on the sleeves orbarrels, and to re-rnelt the initial solid flux envelope which forms onthe sleeves or barrels when initially immersed. The actual time ofimmersion will, of course, vary with the size and composition of theflux bath, and the size and physical character of the ferrous member tobe treated and the temperature drop, if any, of the bath. If the sleevesor barrels have been previously hardened and tempered to a specifieddegree of hardness, it is preferred that the immersion time be kept to aminimum in order to maintain the hardness value close to the originalhardness of the member at the conclusion of the casting operation. Ithas been found that in commericial practice using large flux baths andtreating large heat treated barrels of approximately wall thickness,about 3 to 4 minutes (usually about 3 /2 minutes) in the flux bath issufficient for adequate flux treatment.

When treated in the foregoing manner, the ferrous sleeves or barrelswill have a layer of fluent flux composition of sufiicient thickness toenable them when placed immediately after fiuxing in molds into whichmolten aluminum (1220 F. melting point) at a temperature substantiallybetween 1325 F. and 1425" F. and preferably between 1350" F. and 1400 F.is poured, to obtain a good alloy bond between the ferrous metalsurfaces and the aluminum when the latter is solidified.

The time interval between removal of the fluxcoated sleeves from thefiux bath and start of pouring of the molten aluminum is also essentialof control. In general, the time interval should be short enough toavoid cooling down of the sleeve to a point where substantial freezingor solidification of the flux takes place, or stated otherwise, to acondition where the flux on the sleeve is no longer of fluent characteror cannot be rendered fluent on contact with the molten aluminum. Ingeneral, it has been found that an interval less than 40 seconds ispreferred for best results.

The low temperature limit of the flux bath given above is very importantto control in order to avoid an incomplete bond, for example, bysolidification of the molten aluminum on contact with the ferrous metalfollowing completion of the fluxing step and contacting of the ferrousmember in the mold by the molten aluminum. If the temperature of theflux bath is substantially below about 1340, for instance 1300-1320 F.,prior to immersion, solidification on contact can occur to prevent a.good alloy bond between the ferrous metal and the cast aluminum. Forexample, this may be the case where proper allowance is not made for adrop in the temperature of the bath due to immersing a cold barrel andbringing it up to the lowered bath temperature and which drop in thecase of small baths may be between 50 F. to 75 F. or where there is asubstantial drop in the temperature of the barrel due to too long aninterval between dipping and pouring. Moreover, the lower temperature ofthe flux may decrease the viscosity of the flux film to a point where itis not readily washed away by the rising level of aluminum on pouringinto the mold, thus presenting a barrier between the aluminum and steelat the interface. 1340 F. to a temperature in the order of 1300 F. canbe tolerated, for example, in the case of large furnaces (600 lbs.)where little drop occurs or if the elapsed time between removing theferrous body from the flux Some deviation below bath and pouring of themolten aluminum is made an absolute minimum, for instance, between aboutto seconds by fast handling of the parts and mold and rapid pouring ofthe aluminum, or even as low as 1250 F. when an aluminum alloy isemployed as hereinafter described.

The upper limit temperature of the flux bath is also critical. If thetemperature is too high, the resultant flux will be too fluent and theblanket it forms on the barrel will be thin and may not completelyprevent oxidation from occurring. It would not be practical to employlarge amounts of zinc chloride at these temperatures to correct thiscondition. Moreover, in many instances the ferrous body has beenpreviously brought to a particular condition of hardness ormicrostructure by preheating and tempering, and if the temperature ofthe flux bath is too high, sufficient heat may be transferred to theferrous body by the flux to raise its temperature above the criticalpoint of the material such that its microstructure changes to austenite,and upon subsequent quenching, to martensite with a resultant increasedhardening of the ferrous body. This may be the cause of tool breakage insubsequent machining operations. In general, for example, where barrelsof 2832 Rockwell C hardness are to be muffed, an upper temperatureexceeding 1360" F. will produce a sharp increase in hardness of mostalloy steels.

The optimum temperature range of the flux bath is also somewhatdependent upon the amount of zinc chloride in the composition, thisingredient, having in addition to its fluxing properties, the effect ofcontrolling the viscosity of the flux composition. For example, we haveobserved that with a new bath high in cryolite (25%) and containing byweight 25% or more zinc chloride, a commercially satisfactory aluminumalloy bond may not be obtained, if the fiux bath is at a temperature of1340 F. because the resultant flux layer obtained on immersing .theferrous member in the flux bath may be too thick,

but that a good alloy bond will'be obtained if the flux bath temperatureis in such cases made between about 1375" F. to 1400 F. or even higher,for instance, 1425 F. where the cold barrel effects a substantialtemperature drop in the bath upon immersion. It has been further noted,however, that if the fiux bath has been heated for a number of days atthe higher temperature, some of the zinc chloride escapes as fumes andsome cryolite settles out as the principal constituent of the sludge inthe bottom of the furnace. If an appreciable reduction in the zincchloride content occurs, for example, to about by weight, the thicknessof the flux film formed on the ferrous members will decrease, even withthe bath at a temperature of 1340 F., to a point where it may be readilywashed from the surface of the ferrous body by the molten aluminum and agood aluminum alloy bond be effected. Hence the temperature of the bathmay be thereafter lowered to 134 F. if desired.

The optimum temperature of the flux bath is likewise influenced to someextent by the amount of cryolite present in the composition. Thisessential ingredient, which promotes wetting and dissolves oxides, hasthe further effect when used in large amount, of mechanically thickeningthe flux composition. Accordingly, a somewhat higher bath temperature ispreferred when large amounts of cryolite are employed and thetemperature of the bath may again be lowered when some of this fluoridesalt is lost, as noted above, by sludging.

Based upon our observations, the preferred temperature range for theflux bath will be between about 1330 .F. and about l400 F. (l360 F.maximum if hardening is a factor), and the preferred composition forlarge scale operations will be one preferably containing the follow-.ing essential ingredients:

6 Parts by weight Sodium chloride about 25 to 35 Potassium chlorideabout 25 to 35 Natural Greenland cryolite -about 9 to 20 Zinc chlorideabout 15 to 25 These proportions of the essential ingredients provide awider latitude in timing of the various operations.

The cost of the flux bath composition may be somewhat reduced byreplacing a portion of the natural Greenland cryolite with a syntheticor reduction grade cryolite and replacing minor portions of one or moreof the other essential salts of the composition by other salts, forexample, calcium chloride. It is preferred, however, that the amount ofsubstitute cryolite in the composition should not exceed about 50% asthe present commercial grade of synthetic cryolite is an impuresubstance, and the presence of too great a quantity adversely affectsthe alloy bond between the aluminum and ferrous metal. Likewise, it ispreferred in commerical operations that the calcium chloride be addedafter the previously named essential ingredients of the composition havebeen thoroughly mixed and charged into the furnace and the bath ismolten. The amount added preferably will not exceed about 2 /2 to 5percent by weight of the total charge in the furnace. It has been notedthat if the amount of cryolite in the composition has been reducedsubstantially below about 10 percent by weight, the alloy bond betweenthe aluminum and ferrous metal will be adversely affected and theminimum percentage of this essential ingredient should bere-established.

As will be evident from the previous discussion of the flux composition,that the zinc chloride and cryolite contents do not remain constantduring extended operations, and a control of the composition istherefore preferably provided to compensate for losses in thecomposition due to these ingredients. Various procedures were tried. Byone method, additions of one or both of the critical ingredients, basedupon chemical analysis, were made to the bath when tests indicated thatthe content of these ingredients had dropped to a point where anunsatisfactory bond between the aluminum and the steel would beobtained. This mode of bringing the bath back to its originalcomposition was not found commercially expedient because considerableloss of zinc chloride resulted from excessive fuming when largeadditions of zinc chloride were made and because the added cryolite didnot readily go into solution and sludged heavily.

A second method employed with better results was to ladle outapproximately half of the bath content when failures of bond seemedimminent and to then restore the bath to its proper level by adding newmix to the remainder. This method was also not considered good enoughfor commercial operations.

A much improved method of control was then evolved by which dailyadditions of flux composition were made to the bath to restore its leveland character. In this connection it was found that in a 600-poundfurnace, about 35 pounds (about 5%) of ready mixed salt were requiredeach day for makeup, primarily to correct for drag-out losses. Moreover,it was noted from accumulated chemical data, that the cryolite loss wasapproximately 2% by weight per day and that of zinc chlorideapproximately 1% by weight per day. The control effected was to add 35pounds of makeup mixture per day comprising 26 pounds of ready mixedsalt, 6 pounds of cryolite, and 3 pounds of zinc chloride. This dailyaddition effectively counteracted the cryolite and zinc chloride lossesand provided a satisfactory bond each day of operation. The amount ofmakeup was, moreover, varied depending upon the chemical analysis of thebath, this amount sometimes exceeding the 35 pounds basic addition, inwhich case a portion of the bath was ladled out to provide a properoperating level after additions.

As a result of further observations, a still more flexible system ofcontrol requiring no ladling out of flux and facilitatinga closercontrol of the composition was evolved for making up cryolite and zinzchloride losses.

It was noted, for example in connection with a new 600- pound furnace,that if it was loaded with fresh salt, satisfactory bonding operationscould not be commenced during an initial 48-hour period due to seepageof salt into the porous refractory of the furnace to establish a sealand heavy sludging during this period. During this two-day period, thebath is a murky, non-translucent appearing mass. However, thereafter itchanges to a clear translucent body making visible the bottom of theelectrodes. When the latter stage is reached, it is an indicator thatsatisfactory casting operations productive of excellent bonds may beundertaken.

It was also observed that if the starting cryolite content was 25% byweight, this ingredient rapidly settled out and dropped to 20% and belowafter a few days, if the bath had little agitation but if mechanicalagitation of the bath is provided, this settling out was at a muchslower rate.

It has been pointed out above that with normal production rates,approximately 35 pounds of salt were required for makeup purposes.Employing this factor and a pre-mixed salt having substantially thefollowing composition:

Percent by weight Sodium chlorid 27 /2 Potassium chlorid 27 NaturalGreenland cryolite 20 Zinc chloride 25 As the starting and/or additivemixture, the following control was evolved.

If the daily check of the flux bath showed a cryolite content between16% and 25% by weight, no addition of salt was made. Each day thecryolite content was between l2 /z% and 16% by weight, a 35-pound batchof salt made up of 20% by weight cryolite and 80% by weight of theforegoing pre-mix was added. Each day the cryolite content of the'bathon checking was found to be between 11% and 12 /z%, a 35-pound batch ofsalt made up of 30% cryolite and 70% of the above premix salt was added.If on the daily check the cryolite content fell below 11%, a 35-poundbatch of salt made up of 40% cryolite and 60% of the pre-mix salt wasadded.

By this method of control of the cryolite constituent of the bath it wasfound that additions of zinc chloride are seldom necessary other than bythe pre-mixed makeup salt added to the cryolite when making additions ofthat ingredient. However, if the zinc chloride content dropped below 19%by weight assuming an original content of 25% by weight, additions ofzinc chloride were preferably made as a mixture thereof with theforegoing pre-mix salt and cryolite, and in quantities not exceeding 20%by weight of the total salt addition. This procedure for adding zincchloride restores the quantity in the bath to above 19%. Experience hasshown that such an amount produces a flux bath having better fluidity.The described method of adding zinc chloride also eliminates excessiveloss of this ingredient by smoking when the addition is made.

It will be understood that the daily addition of flux is not limited tothe 35-pound amount based upon experience with a furnace capable ofhandling a 600-pound charge of salt but that this amount may be variedas conditions show the need for greater quantities to restore the bathlevel. However, it is preferred that no greater amount than 70 pounds beadded in one day to a furnace of 600 pounds capacity and then only inbatches where the direct cryolite addition is no greater than 30%, forexperience has shown that larger direct cryolite contents may causeexcessive sludging.

By using the described control it was found possible to maintain theamount of cryolite in the bath at all times between 11% and 14% and theamount of zinc chloride between 19% and 24% and obtained a bond of thealuminum to the ferrous member in all operations. Obviously, theremainder of the bath comprised the other essential ingredients sodiumchloride and potassium chloride and when included such additions ascalcium chloride or other salts to the degree previously indicated.

The fiuxing of ferrous bodies by our invention may be carried out withbest results if the surface of the ferrous metal is roughened, forexample, by grit blasting to obtain a larger surface area of the ferrousmetal for exposure to the flux and consequently to the aluminum therebymaking a stronger bond possible. Moreover, with such a greater surfacearea of roughened character, there is less tendency for the fluent fluxto run off or to become too thin during the casting procedure,particularly in the interval between completion of the fluxing step andpouring of the molten aluminum. It will be understood, however, thatgood bonds may be obtained by the processes described herein withoutgrit blasting by using either ground or turned surfaces.

It may also be noted that one of the critical aspects of the processingis the temperature of the sleeve at which the molten aluminum makescontact with the steel surface. It is difiicult because of manyvariables present to determine this temperature and hence in theforegoing description other temperature indicators have been employed.However, it is believed that the temperature of the sleeve should be oneat least above the melting point of the aluminum (1220 F.) and may serveas an additional control guide.

Prior to starting casting operations it is also preferred that the moldsbe preheated as by gas torch to between 500700 F. This does not have tobe repeated once casting has begun as enough heat remains in the moldsafter casting without again preheating. The molds are also preferablycleaned after each casting operation by blowing off with a light streamof water. The steam formed by this application of water seems to breakaway the salt accumulation on the side walls of the mold and provides abetter operation than that obtained with a mold wash, for instance ofthe graphite type. In fact the use of a stopoif paint such as Pyrornarkat the tops of the barrels to prevent bonding of the aluminum is alsofound to be unnecessary, as any excess aluminum at the top of thecasting can be machined off and no difiiculty experienced even at thebond where an end feed tool is used to cut below the aluminum-steelinterface. The hard brittle Fe-Al compound at the bond breaks up aheadof the edge of the cutting tool.

For a number of reasons, it is often desirable to start cooling of themuffed cylinders after pouring of the aluminum has begun. This isaccomplished by an air-water vapor spray directed against the interiorof such cylinders. This cooling promotes directional solidification ofthe aluminum and thereby avoids shrinkage cavities. Moreover, suchcooling prevents distortion of the ferrous metal and aids in maintaininga proper hardness level where such is necessary. In the latterconnection, if the part is not cooled, heat imparted by the molten metalmay maintain its temperature within the tempering range for a sufiicienttime to decrease the hardness of the previously hardened ferrous memberto a degree below its desired hardness specification.

Where it is desired to provide a longer cooling period for the moltenaluminum after pouring in which it remains in a molten condition so thatthe flux may be more readily completely displaced before the aluminumsolidifies, a lower melting point aluminum composition may be used. Sucha composition may be obtained by the addition of silicon, tin or otherelements. For example, when used in amounts approximately 11% by weightof the composition, silicon will provide a melting point as low as 1070F. Lesser amounts will, of course, determine the temperature for amelting point between 1070 F. and

1220 The use of silicon in the aluminum melt has a further advantage ofproviding a thinner and stronger alloy bond between the cast Yayer andthe ferrous metal surface.

For the purpose of giving those skilled in the art some betterunderstanding of the posibilities of our invention, the followingillustrative examples are given:

Example I Sodium chloride (NaCl) 24.5 Potassium chloride (KCl) 24.5 Zincchloride (ZnCl 24.5 Natural Greenland cryolite (Na AlF 245 Calciumchloride (Cacl 2.5

When the sleeve reached the temperature of the bath, it was immediatelyremoved and placed in a steel mold of a size to form upon casting analuminum muif thick and 4" long at one end of the sleeve. Within 31seconds of removal of the sleeve from the bath, molten aluminum of about1220 F. melting point and at a temperature of 1400 F. was poured intothe mold around the sleeve. About 24 seconds was utilized for pouring.The cast member was then permitted to air cool. Visual and microscopicexamination of the alloy bond between the aluminum and steel disclosedthat an excellent alloy bond was obtained. It was also evident there,had been excellent Wetting of the steel, and that the alloy bond wascontinuous, complete and free of any flux or oxide inclusions.

Example II A steel sleeve of the character described .in Example I wasprovided with a cast aluminum .muff as there described, the molten fluxbath in this example being maintained at a temperature of about 1350 F.The composition of the bath was substantially as follows:

Parts by weight Sodium chloride 40 Potassium chloride 40 NaturalGreenland cryolite 20 Example III An aluminum muff was cast about asteel sleeve of the character described in Example No. l and in themanner there stated, the flux being maintained at 1400 F., and themolten aluminum having a melting point of about 1220 F. and a workingtemperature of about 1400 F. The composition of the flux bath wassubstantially as follows:

Parts by weight Sodium chloride 7 Potassium chloride 44 Zinc chloride 34Natural Greenland cryolite '10 The time interval betwen removal ofthe'sleeve from the flux bath and the start of pouring was 30 seconds,and the pouring time was 10 seconds. Visual and microscopic examinationdisclosed a good bond and good wetting.

Example IV A steel sleeve of the size described in Example I was fluxedand provided with a cast aluminum muffin the manner there stated, usinga flux bath maintained at a temperature of 1400 F. and molten aluminumhaving a melting point of 1220 F. and a working temperature of about1400 F. The composition of the flux bath was substantially as follows:

Parts by weight Sodium chloride '25 Potassium chloride 25 Zinc chloride25 Natural Greenland cryolite 25 The time interval between removing thesleeve from the fiux bath and start of pouring was 30 seconds. Thepouring time was 13 seconds. Visual and microscopic examinationdisclosed good wetting and an excellent alloy bond.

Example V A steel sleeve of the character described in Example I wasprovided with a coating of flux and a cast aluminum muff in the mannerthere stated, the flux bath being maintained at a temperature of 1300 F.and the molten aluminum having a melting point of about 1220 F. and aworking temperature of about 1400 F. The composition of the fiux bathwas substantially as follows:

Parts by weight Sodium chloride 35 Potassium chloride 35 Zinc chloride15 Natural Greenland cryolitc 15 The elapsed time between removal of thesleeve from the bath and the start of pouring was 11 seconds, and thepouring time was 8.5 seconds. Visual and microscopic examinationdisclosed a good alloy bond of about .001" thickness.

Example VI A steel sleeve of the character described in Example I wasfiuxed and provided with a cast aluminum muff as there describedutilizing a flux bath at a temperature of about 1400 F. and moltenaluminum having a melting point of about 1220" F. at a workingtemperature of about 1400 F. The flux composition was substantially asfollows:

Parts by weight Sodium chloride '35 Potassium chloride 35 Zinc chloride15 Natural Greenland cryolite 15 The elapsed time between removal of thesleeve from the fiux and the start of pouring was 30 seconds, and thepouring time was 10.5 seconds. Visual and microscopic examinationdisclosed a good alloy bond having about .001" thickness.

Example VII 111 of the sleeve. The flux bath had substantially thefollowing composition:

Parts by weight Sodium chloride 25 Potassium chloride 25 Zinc chloride25 Natural Greenland cryolite 25 A steel barrel of the character of thepreceding exam ple was immersed and heated in a molten flux bathmaintained at 1350 F. in an Ajax submerged electrode salt bath furnacehaving a capacity of 600 lbs. of salt. The flux had substantially thefollowing composition:

Parts by weight Potassium chloride 35 Sodium chloride 35 Zinc chloride19 Natural Greenland cryolite 11 As soon as the sleeve reached thetemperature of the bath, which required about 3% minutes immersiontherein, it was immediately removed and placed in a steel mold fixtureinto which molten aluminum having a melting point of about 1220 F. and aworking temperature of about 1350 F. was poured within 20 seconds of thetime the sleeve was removed from the bath, the pouring time being about8 seconds. An excellent alloy bond was obtained.

Example IX A shouldered steel barrel of about 5% diameter with a wallthickness of about 3 inch, a inch flange and a length of about 10 incheswas sand blasted in a Wheelabrator cabinet on its exterior surface areato which an aluminum mufi is to be cast. It was then placed in a Detrexdegreaser to remove any grease, and following this painted with a pyropaint to protect the areas to which the aluminum was not to bond.

The barrel was then immersed in a flux bath of molten salt flux heatedto a temperature of 1400 to 1425 F. in an immersed electrode Ajax"electric salt bath furnace of 185 lbs. capacity and kept immersed for 3minutes. The temperature of the barrel at the elapsed time, asdetermined by a thermocouple attached to the side wall of the barrelduring immersion, was between 1340 to 1360 F. There was a drop of 50 to75 F. in the bath temperature experienced on immersion.

The flux bath was prepared by thoroughly mixing together substantially:

Parts by weight Sodium chloride Potassium chloride 25 Zinc chloride 25Natural Greenland cryolite 25 temperature between 1325 and 1350 F.prepared from 99% pure ingot having a melting point of about 1220', F.was immediately poured in the mold by hand ladles to a height of 6 /2".Pouring of the aluminum was started within 25 seconds from the time thebarrel was removed from the hot salt flux and pouring continued asrapidly as possible until the mold was topped. About 10 seconds wasrequired for filling the mold. An operator stood by with a ladle ofaluminum to fill in any shrinkage cavities developed duringsolidification of the aluminum.

During pouring commencing when the mold was half filled, the barrel wasair-water cooled by an air-water vapor spray directed against the insidethereof. After the aluminum solidified, the barrel was removed from thefixture and quenched in oil. Examination of the bond disclosed it to beexcellent.

Example X A shouldered steel barrel of about 5%" inside diameter andbetween V to wall thickness and a length of about 10%", was roughmachined from forgings of an SAE 8640 or AISI TS-8640 or SAE 4140 steeland heat treated, austenitized, quenched in oil, and tempered to ahardness of 28 to 32 Rockwell C. The barrel was then cleaned in a Mahon"washer to remove any grease or dirt, then shot blasted in a blastcabinet to blast clean the outside of the barrel and remove any shinefrom the surfaces to be aluminum muffed.

The barrel was immersed in a flux bath of molten salt flux heated to atemperature between 1330 F. and 1350 F. preferably 1340 F. in animmersed electrode Ajax electric salt bath furnace of 600 lb. capacityand kept immersed for 3% minutes. The flux bath was prepared from ahomogeneous mixture of substantially the following ingredients insubstantially the amounts stated, these ingredients being in granularform of 50 to 200 mesh and of 99% plus purity:

Parts by weight Sodium chloride 27% Potassium chloride 27%. Zincchloride 25 Natural Greenland cryolite 20 After the bath was molten,approximately 2 /2% by Weight of calcium chloride, based upon the weightof the total charge, was added.

The flux-treated barrel was then removed from the hot salt flux andpromptly placed in a preheated l-luckins mold fixture previously heatedto a temperature between 500 to 700 F. and constructed to enable analuminum muff about 6" long and H 1 thick, and weighing about 19 lbs. tobe cast around the barrel. Molten aluminum at a temperature between 1315F. and 1335 F. prepared from 99% pure ingot having a melting point ofabout 1220 F. was immediately poured into the mold with hand ladles toabove the muff area and topped to prevent shrinkage cavities in themuff. Air-water cooling of the inside of the barrel was commenced duringpouring, by an air-water spray applied to the inside of the barrel whenthe mold was filled to a height of 2" to 3" of aluminum. Pouring of thealuminum was com mcnced promptly, i.e., between 10 to 20 seconds afterthe barrel was removed from the salt flux bath (the average for a runwas 15 seconds) and pouring made continuous during the entire pouringcycle. The time to fill the mold with molten aluminum was between 6 to10 seconds (the average for a run was 8 seconds), this time interval notincluding the time required for topping off the mold. The air-waterspray cooling was provided by a movable spray head operating with an airline pressure of 30 to 40 pounds per square inch, and arranged to moveupwardly in the barrel at a rate to require between 2% to 2 /2 minutesto move over the cast area. The rate of water flow in the head wasadjusted such that no actual streams of water were ejected from thespray head, but rather the water was in the form of vapor. Moreover, thehead was adjusted so that the vapor was not excessive to the extent ofspraying over into the molten aluminum on pouring.

After the aluminum had solidified, the barrel was removed from the moldand quenched in tap water.

Examination of the cast muff showed an excellent continuous bond formedwith the steel barrel.

From the above description of our invention and examples, it willbe'evident that various modifications and substitutions will be obviousand others will readily suggest themselves to those skilled in the art,all however without departing from the spirit and scope of ourinvention.

We claim:

1. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith comprising immersing said body in a bath of fluent molten fluxhaving a temperature between l250 F. and l450 F2, and consistingessentially of cryolite and chlorides, maintaining said body in saidbath for a time interval suflicient to provide said body when withdrawntherefrom with a continuous layer of said flux on the portion of thebody where it is to be aluminum faced, said body when withdrawn being ina heated condition and said flux thereon being fluent, withdrawing saidbody from the flux bath and positioning the flux layered body in a moldproviding a cavity adjacent said body shaped to form said facing, andwhile said flux of said flux layer is still fluent pour ing moltenaluminum at a temperature between 1325 F. and 1425 F. into said cavityto form said facing, said molten aluminum displacing said fluent fluxahead of it in the cavity and forming when set a ferro-aluminum alloybond with said body.

2. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith comprising immersing said body in a bath of fluent molten fluxhaving a temperature between 1250 F. and 1450 F., and consistingessentially of cryolite and chlorides, maintaining said body in saidbath at least until the temperatures of said body and of the bath aresubstantially the same whereby to provide said body when withdrawntherefrom with a continuous layer of said flux on the portion of saidbody where it is to be aluminum faced, said body when withdrawn being ina heated condition and said flux thereon being fluent, withdrawing saidheated body with its layer of fluent flux from the flux bath andpositioning the flux layered body in a mold providing a cavity adjacent.said body shaped to form said facing, and while the flux of said fluxlayer is still fluent pouring molten aluminum at a temperature between1350" F. and 1400 F. into said cavity to form said facing, said moltenaluminum displacing said fluent flux ahead of it in the cavity andforming when set a ferroaluminum alloy bond with said body.

3. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith comprising immersing said body in a bath of fluent molten fluxhaving a temperature between 1250 F. and 1450 F. and consistingessentially of cryolite and chlorides, maintaining said body in saidbath for at least about three to 'four minutes whereby to provide saidbody when withdrawn therefrom with a continuous layer of said flux onthe portion of said body where it is to be aluminum faced, said bodywhen withdrawn being in a heated condition and said flux thereon beingfluent, withdrawing said body from the flux bath and positioning theflux layered body in a mold providing a cavity adjacent said body shapedto form said facing, and while the flux of said flux layer is stillfluent pouring molten aluminum at-a temperature between 1325 F. and 1425F. into 14 said cavity to form said facing, said molten aluminumdisplacing said fluent flux ahead of it in the cavity and forming whenset a ferro-aluminum alloy bond with said body.

4. The process of producing a duplex metal structure comprising aferrous metal body and 21 facing of cast aluminum having an alloy bondtherewith comprising immersing said body in a bath of fluent molten fluxof the salt type having a temperature between l250 F. and 1450 F saidflux consisting essentially of the following ingredients insubstantially the amounts stated:

Parts by weight Sodium chloride 7 to 40 Potassium chloride 24 to 44Natural Greenland cryolite 9 to 25 Zinc chloride 0 to 34 maintainingsaid body in said bath for at least about three to four minutes wherebyto provide said body when withdrawn therefrom with a continuous layer ofsaid fluent flux on the portion of said body where it is to be aluminumfaced, withdrawing said body from the flux bath and positioning the fluxlayered body in a mold providing a cavity adjacent said body shaped toform said facing, and while the flux of said flux layer is still fluentpouring molten aluminum at a temperature between 1325 F. and 1425 F.into said cavity to form said facing, said molten aluminum displacingsaid fluent flux ahead of it in the cavity and forming when set aferro-aluminum alloy bond with said body.

5. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith comprising immersing said body in a bath of fluent molten fluxof the salt type having a temperature between l250 F. and 1450 F., saidflux consisting essentially of the following ingredients insubstantially the amounts stated:

Parts by weight Sodium chloride 7 to 40 Potassium chloride 24 to 44Natural Greenland cryolite 9 to 25 Zinc chloride 0 to 34 maintainingsaid body in said bath for at least about three to four minutes wherebyto provide said body when withdrawn therefrom with a continuous layer ofsaid fluent flux on the portion of said body where it is to be aluminumfaced, withdrawing said body from the flux bath and positioning the fluxlayered body in a mold providing a cavity adjacent said body shaped toform said facing, while the flux of said flux layer is still fluentpouring molten aluminum at a temperature between 1325 F. and 1425 F.into said cavity to form said facing, said molten aluminum displacingsaid fluent flux ahead of it in the cavity and forming when set aferro-aluminum alloy bond with said body, and commencing pouring of saidmolten aluminum within forty seconds of removal of said body from saidflux bath.

6. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith comprising immersing said body in a bath of fluent molten fluxof the salt type having a temperature between 1250 F. and 1450 F., saidflux consisting essentially of the following ingredients insubstantially the amounts stated:

Parts by weight Sodium chloride 25 to 40 Potassium chloride 25 to 40Natural Greenland cryolite 9 to 25 Zinc chloride 10 to 30 maintainingsaid body in said bath for at least about three to four minutes wherebyto provide said body when withdrawn therefrom with a continuous layer ofsaid fluent flux on the portion of said body where it is to be aluminumfaced, withdrawing said body from the flux bath and positioning the fluxlayered body in a mold providing a cavity adjacent said body shaped toform said facing, while the flux of said flux layer is still fluentpouring molten aluminum at a temperature between 1325" F. and 1425 F.into said cavity to form said facing, said molten aluminum displacingsaid fluent flux ahead of it in the cavity and forming when set aferro-aluminum alloy bond with said body, and commencing pouring of saidmolten aluminum within forty seconds of removal of said body from saidflux bath.

7. The process of producing a duplex metal structure comprising ahardened ferrous metal body and a facing of cast aluminum having analloy bond therewith comprising immersing said body in a bath of fluentmolten flux of the salt type having a temperature between 1340" F. and1360 B, said flux consisting essentially of the following ingredients insubstantially the amounts stated:

Parts by weight Sodium chloride 7 to 40 Potassium chloride 24 to 44Natural Greenland cryolite 9 to 25 Zinc chloride to 34 maintaining saidbody in said bath for at least about three to four minutes whereby toprovide said body when withdrawn therefrom with a continuous layer ofsaid fluent flux on the portion of said body where it is to be aluminumfaced, withdrawing said body from the flux bath and positioning the fluxlayered body in a mold providing a cavity adjacent said body shaped toform said facing, while the flux of said flux layer is still fluentpouring molten aluminum at a temperature between 1325 F. and 1425 F.into said cavity to form said facing, said molten aluminum displacingsaid fluent flux ahead of it in the cavity and forming when set aferro-aluminum alloy bond with said body, and commencing pouring of saidmolten aluminum within forty seconds of removal of said body from saidflux bath.

8. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith comprising immersing said body in a bath of fluent molten fluxof the salt type having a temperature between 1330 F. and 1400 F., saidflux consisting essentially of the following ingredients insubstantially the amounts stated:

Parts by weight Sodium chloride 25 to 35 Potassium chloride 25 to 35Natural Greenland cryolite 9 to 20 Zinc chloride to 25 maintaining saidbody in said bath for at least about three to four minutes whereby toprovide said body when withdrawn therefrom with a continuous layer ofsaid fluent flux on the portion of said body where it is to be aluminumfaced, withdrawing said body from the flux bath and positioning the fluxlayered body in a mold providing a cavity adjacent said body shaped toform said facing, while the flux of said flux layer is still fluentpouring molten aluminum at a temperature between 1325 F. and 1425 F.into said cavity to form said facing, said molten aluminum displacingsaid fluent flux ahead of it in the cavity and forming when set aferro-aluminum alloy bond with said body, and commencing pouring of saidmolten aluminum within forty seconds of removal of said body from saidflux bath.

9. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith comprising immersing said body in a bath of fluent molten fluxof the salt type having a temperature between l330 F. and 1400 F., saidflux consisting essentially of the following ingredients insubstantially the amounts stated:

Parts by weight, Sodium chloride 25 to'35 Potassium chloride 25 to 35Natural Greenland cryolite 9 to 20 Zinc chloride 15 to 25 Calciumchloride 2.5 to 5 maintaining said body in said bath for at least aboutthree to four minutes whereby to provide said body when withdrawntherefrom with a continuous layer of said fluent flux on the portion ofsaid body where it is to be aluminum faced, withdrawing said body fromthe flux bath and positioning the flux layered body in a mold providinga cavity adjacent said body shaped to form said facing, while the fluxof said flux layer is still fluent pouring molten aluminum at atemperature between 1325 F. and 1425 F. into said cavity to form saidfacing, said molten aluminum displacing said fluent flux ahead of it inthe cavity and forming when set a ferro-aluminum alloy bond with saidbody, and commencing pouring of said molten alu minum within fortyseconds of removal of said body from said flux bath.

10. The process as claimed in claim 9 wherein up to 50% of the cryolitein the composition comprises cryolite selected from the group consistingof synthetic and reduction grade cryolites.

11. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith comprising immersing said body in a bath of fluent molten fluxhaving a temperature between 1250 F. and 1450 F., and consistingessentially of cryolite and chlorides, maintain ing said body in saidbath for at least about three to four minutes whereby to provide saidbody when withdrawn therefrom with a continuous layer of said flux onthe portion of said body where it is to be aluminum faced, said bodywhen withdrawn being in a heated condition and said flux thereon beingfluent, withdrawing said body from the flux bath and positioning theflux layered body in a mold providing a cavity adjacent said body shapedto form said facing, and while the flux of said flux layer is stillfluent pouring molten aluminum alloy containing silicon in an amount nogreater than about 11% by weight of the metal composition and at atemperature between 1300 F. and 1400 F. into said cavity to form saidfacing, said molten aluminum displacing said fluent flux ahead of it inthe cavity and forming when set a ferro-aluminum alloy bond with saidbody.

12. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith, comprising immersing said body in a bath of fluent moltenflux of the salt type having a temperature of about 1400 F., said fluxconsisting essentially of the following compoition:

Parts by weight Sodium chloride About 24.5 Potassium chloride About 24.5Zinc chloride About 24.5 Natural Greenland cryolite About 24.5 Calciumchloride About 2.5

maintaining said body in said bath until the temperature of said bodyand said bath are substantially the same whereby to provide said bodywhen withdrawn therefrom with a continuous layer of said fluent flux onthe portion of said body where it is to be aaluminum faced, withdrawingsaid body from the flux bath and positioning the flux layered body in amold providing a cavity adjacent said body shaped to form said facing,while the flux of said flux layer is still fluent pouring moltenaluminum having a melting point of about 1220 F. and at a temperature ofabout 1400 F. into said cavity to form said facing, said molten aluminumdisplacing said fluent flux ahead of it in the cavity and forming Sodiumchloride About 40 Potassium chloride About 40 Natural Greenland cryoliteAbout 20 maintaining said body .in said bath until the temperature ofsaid body and said bath are substantially the same whereby to providesaid body when withdrawn therefrom with a continuous layer of saidfluent flux on the portion of said body where it is to be aluminumfaced, withdrawing said 'body from the flux bath and positioning theflux layered body in a mold providing a cavity adjacent said body shapedto form said facing, while the flux of said flux layer is still fluentpouring molten aluminum having a melting point of about l220 F. and at atemperature of about 1400 F. into said cavity to form said facing, saidmolten aluminum displacing said fluent flux ahead of it in the cavityand forming when set a ferro-aluminum alloy bond with said body, andcommencing pouring of said molten aluminum within about 9.5 seconds ofremoval of the body from said bath.

.14. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith, comprising immersing said body in a bath of fluent moltenflux of the salt type having a temperature of about 1400 F., said fluxconsisting essentially of the following composition:

. Parts by weight Sodium chloride About 25 Potassium chloride About 25Zinc chloride About 25 Natural Greenland cryolite About 25 maintainingsaid'body in said bath until the temperature of said body and said bathare substantially the same whereby to provide said body when withdrawntherefrom with a continuous layer of said fluent flux on the portion ofsaid body where it is to be aluminum faced, withdrawing said body fromthe flux bath and positioning the flux layered body in a mold providinga cavity adjacent said body shaped to form said facing, while the fluxof said flux layer is still fluent pouring molten aluminum having amelting point of about l220 F. and at a temperature of about 1400 F.into said cavity to form said facing, said molten aluminum displacingsaid fluent flux ahead of it in the cavity and forming when set aferro-aluminum alloy bond with said body, and commencing pouring of saidmolten aluminum within about 30 seconds of removal of the body from saidbath.

15. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith, comprising immersing said body in a bath of fluent moltenflux of the salt type having a temperature of about between 1300 F. and1400 F., said flux consisting essentially of the following composition:

Parts by weight Sodium chloride About 35 Potassium chloride About 35Zinc chloride About 15 Natural Greenland cryolite About 15 maintainingsaid body in said bath until the temperature of said body and said bathare substantially the same whereby to provide said body when withdrawntherefrom with a continuous layer o'f said'fluent' flux on the portionof said body where it is'to be aluminum faced, withdrawing said bodyfrom the flux bath and positioning the flux layered body in a moldproviding a cavity adjacent said body shaped to form said facing, whilethe flux of said flux layer is still fluent pouring molten aluminumhaving a melting point of about l220 F. and at a temperature of about1400" F. into said cavity'to form said facing, said molten aluminumdisplacing said fluent flux ahead of it in the cavity and forming whenset a ferro-aluminum alloy bond with said body, and commencing pouringof said molten aluminum within about 11 to 30 seconds of removal of thebody from said bath.

16. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith, comprising immersing said body in a bath of fluent moltenflux of the salt type having a temperature of about 1400 F., said fluxconsisting essentially of the following composition:

Parts by weight Sodium chloride About 25 Potassium chloride About 25Zinc chloride About 25 Natural Greenland cryolite About 25 maintainingsaid body in said bath until the temperature of said body and said bathare substantially the same whereby to provide said body when withdrawntherefrom with a continuous layer of said fluent flux on the portion ofsaid body where it is to be aluminum faced, withdrawing said body fromthe flux bath and positioning the flux layered body in a mold providinga cavity adjacent said body shaped to form said facing, while the fluxof said flux layer is still fluent pouring molten aluminum having amelting point of about l220 F. and at a temperature of about 1430 F.into said cavity to form said facing, said molten aluminum displacingsaid fluent flux ahead of it in the cavity and forming when set aferroaluminum alloy bond with said body, and commencing pouring of saidmolten aluminum within about 35 seconds of removal of the body from saidbath.

17. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith, comprising immersing said body in a bath of fluent moltenflux of the salt type having a temperature of about 1350" F., said fluxconsisting essentially of the following composition:

Parts by weight Potassium chloride About 35 Sodium chloride About 35Zinc chloride About 19 Natural Greenland cryolite About ll maintainingsaid body in said bath until the temperature of said body and said bathare substantially thesame whereby to provide said body when withdrawntherefrom with a continuous layer of said fluent flux on the portion ofsaid body where it is to be aluminum faced, withdrawing said body fromthe flux bath and positioning the flux layered body in a mold providinga cavity adjacent said body shaped to form said facing, while the fluxof said flux layer is still fluent pouring molten aluminum having amelting point of about l220 F. and at a temperature of about 1325 F. to1350" F. into said cavity to form said facing, said molten aluminum.displacing said fluent flux ahead of it in the cavity and forming whenset a ferro-aluminum alloy bond with said body, and commencing pouringof said molten aluminum within about 20 seconds of removal of the bodyfrom said bath.

18. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith, comprising immersing said body in a bath of fluent moltenflux of the salt type having a temperature of about 1400 F. to 1425 F.,said flux-consisting essentially of the fol- ;lowing composition;

, Parts by weight S i m chloride About 25 Potassium chloride About 25.Zinc chloride About 25 Natural Greenland cryolite About 25 Calciumchloride About 2% maintaining said body in said bath about 3% minuteswhereby to'provide said body when withdrawn therefrom with a continuouslayer of said fluent flux on the portion of said body where it is to bealuminum faced, withdrawing said body from the flux bath and positioningthe flux layered body in a mold providing a cavity ad- "jacent said bodyshaped tofform said facing, while the flux of said flux layer is stillfluent pouring molten aluminum having a melting point of about 1220 F.and at a temperature of about 1325 F. to 1350 F. into said cavity toform said facing, said molten aluminum displacing said fluent flux aheadof it in the cavity and forming when set a ferro-aluminum alloy bondwith said body, and commencing pouring of said molten aluminumgvitllliin about 25 seconds of removal of the body from said 19. Theprocess of producing a duplex metal structure comprising a hardened andtempered ferrous metal body having a hardness of 28 to 32 Rockwell C anda facing of cast aluminum having an alloy bond therewith, comprisingimmersing said body in a bath of fluent molten flux of the salt typehaving a temperature of about 1330 F. to 1350' F., said flux consistingessentially of the following composition:

Parts by weight I Sodium chloride About 27% Potassium chloride About 27/2 Zinc chloride About 25 Natural Greenland cryolite About 20 Calciumchloride About 2% maintaining said body in said bath about 3% minuteswhereby to provide said body when withdrawn therefrom .with a continuouslayer of said fluent flux on the portion of said body where it is to bealuminum faced, withdrawing said body from the flux bath and positioningthe flux layered body in a mold providing a cavity adjacent said bodyshaped to form said facing, while the .flux of said flux layer is stillfluent pouring molten bath.

20. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum having an alloy bondtherewith comprising immersing said body in a bath of fluent molten fluxconsisting essentially of cryolite and chlorides and having atemperature above the melting point of the flux in the order of 1250 F.and not exceeding substantially 1450 F., maintaining said body in saidbath for a time interval suflicient to provide said body when withdrawntherefrom with a continuous adherent layer of said flux on the portionof the body where it is to be aluminum faced, said body when withdrawnbeing in a heated condition and said flux thereon being fluent,withdrawing said body from the flux bath and positioning the fluxlayered body in a mold providing a cavity adjacent said body shaped toform said facing, and while the flux of said layer is still fluentcasting between said body and said mold a facing of molten aluminum at atemperature above its melting point and not substantially exceeding 1425F., said molten aluminum displacing said fluid flux ahead of it in thecavity and forming when set a ferroalummum alloy bond with said body.

21. The process of producing a duplex metal structure comprising aferrous metal body and a facing of c ast aluminum having an alloy bondtherewith compris ng inmersing said body in a bath of fluent molten fluxhaving a temperature between 1250 F. and 1450 F., and consistingessentially of fluorides and chlorides, maintaining said body in saidbath for a time interval suflicient to provide said body when withdrawntherefrom with a continuous layer of said flux on the portion of thebody where it is to be aluminum faced, said body when withdrawn being ina heated condition and said flux thereon being fluent, withdrawing saidbody from the flux bath and positioning the flux layered body in a moldproviding a cavity adjacent said body shaped to form said facing, andwhile said flux of said flux layer is still fluent pouring moltenaluminum at a temperature between 1325 F. and 1425" F. into said cavityto form said facing, said molten aluminum displacing said fluent fluxahead of it in the cavity and forming when set a ferro-aluminum alloybond with said body.

22. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum alloy having an alloybond therewith, comprising immersing said body in a bath of fluentmolten flux consisting essentially of fluorides and chlorides and havinga temperature above the melting points of the flux and aluminum alloyand not exceeding substantially 1450 F., maintaining said body in saidbath for a time interval sufficient to provide said body when withdrawntherefrom with a continuous layer of said flux on the portion of thebody where it is to be aluminum faced, said body when withdrawntherefrom being in a heated condition and said flux thereon beingfluent, withdrawing said body from the said flux bath and positioningthe flux layered body in a mold providing a cavity adjacent said bodyshaped to form said facing, and While said flux of said flux layer isstill fluent casting between said body and said mold a facing of moltenaluminum alloy at a temperature above its melting point and not substantially exceeding 1425 F., said molten aluminum displacing said fluidflux ahead of it in the cavity and forming when set a ferro-aluminumalloy bond with said body.

References Cited in the file of this patent UNITED STATES PATENTS638,961 Cosgrave Dec. 12, 1899 1,749,712 Michel Mar. 4, 1930 1,792,580Fehrenbach Feb. 17, 1931 1,876,073 Player Sept. 6, 1932 1,923,375 HoltAug. 22, 1933 2,101,553 Mattsson Dec. 7, 1937 2,234,904 Pike Mar. 11,1941 2,452,995 Cinamon Nov. 2, 1948 2,544,670 Grange et al Mar. 13, 19512,544,671 Grange et a1 Mar. 13, 1951 2,611,163 Schaeffer Sept. 23, 19522,634,469 Pershing et al. Apr. 14, 1953 2,671,737 .lominy Mar. 9, 1954

1. THE PROCESS OF PRODUCING A DUPLEX METAL STRUCTURE COMPRISING AFERROUS METAL BODY AND A FACING OF CAST ALUMINUM HAVING AN ALLOY BONDTHEREWITH COMPRISING IMMERSING SAID BODY IN A BATH OF FLUENT MOLTEN FLUXHAVING A TEMPERATURE BETWEEN 1250*F. AND 1450*F., AND CONSISTINGESSENTIALLY OF CRYOLITE AND CHLORIDES, MAINTAINING SAID BODY IN SAIDBATH FOR A TIME INTERVAL SUFFICIENT TO PROVIDE SAID BODY WHEN WITHDRAWNTHEREFROM WITH A CONTINUOUS LAYER OF SAID FLUX ON THE PORTION OF THEBODY WHERE IT IS TO BE ALUMINUM FACED, SAID BODY WHEN WITHDRAWN BEING INA HEATED CONDITION AND SAID FLUX THEREON BEING FLUENT, WITHDRAWING SAIDBODY FROM THE FLUX BATH AND POSITIONING THE FLUX LAYERED BODY IN A MOLDPROVIDING A CAVITY ADJACENT SAID BODY SHAPED TO FORM SAID FACING ANDWHILE SAID FLUX OF SAIDFLUX LAYER IS STILL FLUENT POURING MOLTENALUMINUM AT A TEMPERATURE BETWEEN 1325*F. AND 1425*F. INTO SAID CAVITYTO FORM SAID FACING, SAID MOLTEN ALUMINUM DISPLACING SAID FLUENT FLUXAHEAD OF IT IN THE CAVITY AND FORMING WHEN SET A FERRO-ALUMINUM ALLOYBOND WITH SAID BODY.